One of the problems in the solution or slurry polymerization of monomer is the capital costs required in the production thereof. Monomer polymerization using a vapor phase process can be considerably more economical if certain problems inherent in vapor state polymerization can be solved. In vapor state processes using high yield catalysts and cocatalysts, i.e., processes yielding polymer from which catalyst and cocatalyst residues need not be removed, particulate, solid polymer is removed from the reactor and then, after decomposition of the catalyst and cocatalyst, melt extruded along with additives to form commercially useful product. A useful saving on heat requirements can be obtained if the solid particulate polymer is melted directly without intermediate cooling upon leaving the reactor and thereafter all finishing operations carried out on the molten polymer. However, melting of the polymer from the reactor by externally supplied heat is inefficient because of the low thermal conductivity and low rate of heat transfer through such particulate polymeric solids and melted polymer.
Now it has been found that by supplying an important fraction of the additional heat required to raise the temperature of the solid particulate polymer exiting the reactor to above the polymer melting point by an essentially adiabatic polymerization in a post polymerization zone, an extremely efficient method of forming molten polymer suitable for melt finishing results. An additional benefit obtained by such post reactor polymer melting is an improvement in the purity of the final product because the post polymerization melting partially devolatilizes the polymer prior to the catalyst decomposition step. Thus, important economic benefits are realized through savings in energy consumption, raw materials and capital equipment.